The purpose of this study is to determine the mechanism of mechanosensitivity in motile sensory cilia and in certain somatic cilia as well, using three related approaches to achieve these ends. 1. We will continue electrophysiological studies of molluscan gill cilia and other ciliated cells to determine the ionic basis for mechanosensitivity. Intracellular recordings will be made from molluscan gill and echinoderm or other larval ciliated cells under various ionic conditions, establishing requirements for generator and regenerative potential production. To evaluate the importance of cell-cell communication in ciliary coordination, intracellular recording of electrically-coupled cells, with motile cilia under mechanical stimulation, will be performed with two recording electrodes in adjacent and in distant cells, varying the ionic environment and experimentally uncoupling the cells. Molluscan gill abfrontal cells will be used as a model system. Deciliated lateral and abfrontal cells will be studied to determine if the site of mechanical sensitivity is located on the plasma membrane. 2. We will use reconstituted membrane vesicles to characterize the ciliary calcium pump system and determine a possible role of calmodulin. Isolated molluscan gill cilia having very different calcium ion sensitivities will be used as membrane sources for comparison. The vesicle protein composition will be analyzed electrophoretically in detail to determine the presence of characteristic proteins. Ca-ATPase(s) will be purified from ciliary membranes and characterized. Is calcium sensitivity a function of relative transport efficiency? Is Ca-ATPase modulated by either calmodulin or diphosphoinositide? 3. We will prepare gill cilia that are activated by calcium and compare them to cilia that are inhibited by calcium. We will study the ATPase activity of the cilliary axonemes and of the dynein isolated and purified from them, varying calcium ions, calmodulin, and salt conditions. In parallel, we will use dark-field microscopy to determine whether microtubule sliding is under calcium control in these axonemes.